1. Field of Invention
The invention relates to a machine tool, and more particularly to a machine tool for milling and boring workpieces.
2. Discussion of Related Art
Current machine tools designed to process large workpieces, such as aircraft parts, typically have relatively long traveling work tables for accommodating and accurately fixing these large workpieces. They may also have traveling stands that can travel laterally along the workpiece in correspondingly long guide rails and upon which the supporting system of the machining unit is mounted. The basic axes are realized as parallel kinematics and the head axes are designed as serial axes. For example various designs of such a machine tool are produced under the mark TRICEPT(copyright) (Neos Robotics AB Corporation Sweden of Taby, Sweden).
Universal machine tools in which the machining unit carries the milling head in the form of a tripod have been described. See Dr. Werner Eberlein and Ulrich Schleider, xe2x80x9cBearbeitungszentrum mit Tripodentechnikxe2x80x9d [Machining Center Making Use of The Tripod Technology], VDI-Z 143, No.6, pgs. 38-40 (June 2001). The spindle support casing in that device is supported with three degrees of freedom, and moved by three triangular guides by a joint. Each triangular guide is pivoted to an associated linear guiding system. The guiding systems are disposed in a cylindrical receiving body. The integrated slides are moved longitudinally by recirculating ball screws and servo drives. In this system, the working spindle having an integrated drive motor can be moved within a solid angle of 80xc2x0. However, this machine type is designed to machine extremely large-area workpieces, in particular large structural parts, for example, aircraft wings that may have overall lengths of 2.5 m and traveling paths of up to 30 m.
The present invention relates to a program-controlled universal combined milling and boring machine. In one embodiment, the invention has a horizontal base serving as a support for a work table, a machine frame, and a supporting system for at least one spindle head. The spindle head contains a dimensionally stable central tube, a spindle head support mounted on the lower end thereof, three telescopic bars arranged at a solid angle displacement of 120xc2x0 and coupled by means of cardanic mounting to the spindle head support, and a top supporting member having universal bearings for the central tube and for each telescopic bar.
It is one objective of the invention to provide a universal combined milling and boring machine having a compact design and providing a high degree of machining accuracy. The extreme unit rigidity and highly accurate tool positioning afforded by the machine of the present invention are factors contributing to the above objective.
Specifically, this objective may be achieved by the present invention providing the machine frame together with the base as an integrated dimensionally stable support structure. The support structure may have two side walls, a dimensionally stable front traverse and a lower rear wall, and inclining the supporting member of the supporting system between the lower rear wall and the traverse.
The machine frame, together with the integrated base of the work table, provide a box-like shape that affords an extremely high degree of rigidity, thus obtaining maximum machining accuracy. The inclined position of the supporting element for the central tube, along with the machining head and the three telescopic bars, result in a particularly favorable position for the spindle head. They also result in loads that are more uniform as compared to a vertical or horizontal arrangement of the supporting element. The machine tool according to the invention is relatively compact and only requires a relatively small floor space. The advantageous tripod mounting of the machine herein is afforded by the table being fixed on the base.
A preferred embodiment of the invention has a supporting member of the supporting system designed as a flat, dimensionally stable slide and movable in horizontal guides of the traverse and the rear wall by means of a motor. This movability of the slide, and thus also of the machining unit, provides optimum positioning of the machine head relative to the workpiece. Since the masses of the slide and the units supported by it are relatively small and virtually constant, further advantages result for the slide movements, specifically in relation to the design and effectiveness of the drive and control aggregates.
It is preferred that the slide have a generally triangular shape and be supported by its longer rear side by means of two terminal guide elements on a guide rail mounted on the rear wall. On the shorter front side, the slide is preferably supported by means of at least one guiding element on a guide rail attached to the front top traverse. Due to this shape and support of the slide, a favorable transfer of the slide forces occurs during the machining step from slide to machine frame, even if the machining tool is extremely displaced.
One significant feature of the machine tool according to the present invention is the single-part design of the central tube. Previous devices typically have multi-part designs in which the individual parts have to be aligned relative to one another during the assembly and then be fixed. These steps may result in inaccuracies in positioning behavior. Due to the single-part tube design of the present invention, such an alignment step is unnecessary. In addition the positioning accuracy of the universal joints or bearings relative to the telescopic bars, which act as linear guides, is established directly during the manufacturing process. This allows improved tolerances to be achieved.